Method of producing a coating doctor

ABSTRACT

A coating doctor blade having a chamfered face is produced by the steps of forming into a roll a hardened and tempered metal band blank, edge-grinding the blank in the roll, winding off the blank, planing a chamfer surface on one side surface of the blank by moving the blank, in a single pass in the longitudinal direction of the blank, over a single hard metal bit thereby providing a chamfered surface free from scratches and grooves detrimental to the evenness of a coating spread by the resulting doctor blade, and dividing the so-chamfered blank into doctor blades of suitable lengths.

United States Patent l 13,611,841

[7 2] lnventors Karl Erik l-lolger Froden; [56] Reference Cit d gakslm Arne Eriksson, both of Munkfors, UNITED STATES PATENTS we en 2,936,679 5/1960 Thuerwachter 90/24 i 1968 1,404,488 1/1922 51/98 Q 45 Patented 0a. 12, 1971 332%: 3232; L 83 2: [73] Assignee Uddeholms Aktiebolag mger Uddeholm Sweden 3,356,067 12/1967 Krasnow et al. 118/123 1 [32] Priority Nov. 7, 1967 Primary ExaminerBernard Stickney [33] Sweden AttorneyPierce, Scheffler & Parker [31] 15216/67 ABSTRACT: A coating doctor blade having a chamfered face is produced by the steps of forming into a roll a hardened and tempered metal band blank, edge-grinding the blank in the [54] METHOD OF PRODUCING A COATING DOCTOR roll, winding off the blank, planing a chamfer surface on one 2 Chums 3 Drawmg 4 side surface of the blank by moving the blank, in a single pass [52] US. Cl 76/101 R, in the longitudinal direction of the blank, over a single hard 90/24, 1 18/ 123 metal bit thereby providing a chamfered surface free from [5 l] Int. Cl B21k 21/00 scratches and grooves detrimental to the evenness of a coating [50] Field of Search 76/101' spread by the resulting doctor blade, and dividing the so- 90/24.04, 24; l 18/ 1 23; 51/98 chamfered blank into doctor blades of suitable lengths.

PATENTE1111B112191| 1 INVENTORS k H L er- Frode symlkqn rne Erikssor,

I A'bhor g METHOD OF PRODUCING A COATING DOCTOR The present invention is related to a method of producing a coating doctor, one longitudinal edge of which is chamfered to form at least one chamfer face for laying on or stripping off a coating on a material, by way of example a paper web.

The coating doctor produced according to the invention is primarily designed for being utilized within the paper industry for the coating of paper and cardboard but is probably to be relied upon also in other fields where it is required to obtain a smooth laying on or stripping off of a coating, as for example within the graphic arts.

In producing cardboard in accordance with a known method a composition comprising i.a., starch and pigment is laid on by means of a doctor onto a running paper web. The method can either be accomplished in a paper machine or in a separate machine. The doctors used consist usually of a band formed steel tool, one longitudinal edge of which has been chamfered so that they have obtained a chamfered face capable of serving as an active spreading surface during the layingon process.

In using prior art coating doctors there have been great difficulties in obtaining acceptable results with respect to the surface smoothness of the finished material. In installing new doctors it has thus been necessary to discard or qualify as second-rate large material quantities owing to surface defects in the material during long running-in times. It has now been possible to state that these defects have been caused primarily by transverse grooves in the mentioned chamfer surface, which only after a long time of running-in have become such polished by the material web passing by that it will be capable of distributing and spreading out the coating onto the web without any grooves or other defects arising.

To eliminate the fault sources it has previously been tried to hone (polish) the active coating surfaces. The method is, however, costly and does not still give a quite satisfactory result. The removal of remainders of prior grinding scratches has thus not been quite successful in technical/economical practice. For doctors having a great length it has further always been necessary to take into consideration the wear and selfdressing intervals of the disc making an accurate maintenance of a rectilinear edge impossible. The dimensional deviations obtained in grinding are also difficult to remove by honing. As an alternative to honing a chrome coating has also been suggested.

In using coating doctors produced according to the present invention quite superior results are, however, achieved with respect to the smoothness of the finished material, in spite of the fact that the doctors are not more costly but rather cheaper to produce than those previously produced by grinding honing. These advantages which are of such an importance that the method of producing cardboard which is based on the use of doctors may gain a substantially increased application are achieved in accordance with the invention by the fact that said chamfer face has been produced by planing in the longitudinal direction of the doctor whereby disturbing scratches or other machining grooves are avoided. Preferably the chamfer face is produced by planing by means of one or more hard metal bits, preferably, however, through one-chip planing by means of one single hard metal bit.

It is, however, also of importance that not even the surfaces adjacent to the chamfer face exhibits any transverse grooves since otherwise teeth would form in the longitudinal edge lines of the chamfer face which could spoil the spreading out operation. The invention is accordingly also characterized in that also surfaces adjacent to the chamfer face are machined in the longitudinal direction. If it is considered suitable a plurality of chamfer faces may be produced adjacent to each other according to the invention.

Further characteristics and advantages of the invention will appear from the following description in which reference is made to the appended drawing figures of which FIG. I shows diagrammatically the operation known per se of a coating doctor,

FIG. 2 shows in perspective view a portion of a coating doctor according to the invention and FIG. 3 shows the same doctor seen from the side.

By 1 is in FIG. 1 designed a doctor consisting of a bandlike steel tool one longitudinal edge of which is secured in a holder 2. The purpose of the doctor is to spread out a coating 3 onto a web material 4, by way of example a paper web, and abuts to this end in a manner shown in the figure with its other edge towards the web. The coating material may consist, as in the case in the production of cardboard, of for example a composition including clay materials, starch, pigments, etc.

The doctor shown in FIG. 2 and 3 the exterior form of which is per se previously known, exhibits border surfaces of which those in view in FIG. 2 are designed in the following manner:

5: an end surface 6: a side surface 7: an edge surface 8: a chamfer surface What characterizes primarily the invention is the fact that the chamfer face 8 has been produced by planing in the longitudinal direction, more particularly by means of one single planing operation with a hard metal bit. By this process substantially no irregularities arise in said chamfer face 8. The planing is accomplished continuously by winding ofia blank wound up to a roller and hardened, tempered and edgeground, from the roller and passing it beyond the stationary hard metal bit which bevels off the edge so as to obtain the very smooth surface 8 by one single step and subsequently the band is divided up in pieces of a suitable length. The edgegrinding is accomplished while the blank is disposed wound up to a roller and is contrived by moving a grinding tool in such a manner towards the roller that the grinding occurs only a right angles to the diameter of the roller, i.e., corresponding to the longitudinal direction of the wound-up band. Simultaneously as securing thereby that the edge surface 7 will have no transverse grooves the important advantage is also achieved that the edge can be made very straight. Alternatively one may instead edge-grind the blank in a surface grinding machine and subsequently edge plane it so as to remove the grinding pattern. A further method is to accomplish the edge planing without prior grinding.

By the fact that the chamfer face 8 has been produced by longitudinal planing and that nor the edge surface 8 exhibits any transverse grooves the intersection line between the two surfaces will be smooth and free from teeth or notches. This is of a great importance as it is exactly this edge line that is the last to leave contact with the web material running by, see FIG. 1.

It is, however, important that also the intersection line 10 between the chamfer face 8 and the side surface6 of the doctor is free from irregularities. Also this desire can be satisfied according to the invention by having the steel band of which the doctor is produced, cold rolled and mechanically surface machined in a manner to make the rolling and machining directions correspond to the longitudinal direction of the doctor.

While strength and configuration in other respects of the doctor may be varied within a wide range the strength dimensions lie for those purposes which will be considered primarily below I mm. and preferably below 0.7 mm., dimensions being per se common in coating doctors of the present kind. In a doctor manufactured and tested with excellent result the thickness was 0.305 mm. The material consisted of hardened and tempered carbon steel and the chamfer planing was accomplished to a depth to make the width of the remaining edge surface 7 0.12 mm. The angle a was 35.

While a coating doctor manufactured according to the measures indicated above has proved to work in an excellent manner it will be understood that the invention is not limited to these measures. The angle may thus for example be varied most substantially as well as strength and chamfer width of the doctor. Various materials are also conceivable. Beside carbon steel also stainless qualities will thus be taken into consideration as well as other metals than steel at least for certain purposes. It is further possible to modify within the spirit of the in edge-grinding the blank while in the roll, winding off the edge-ground blank and planing a chamber surface on one side surface of the blank by moving the blank, in a single pass in the longitudinal direction of the blank, over a single hard metal bit thereby providing a chamfered surface free from scratches and grooves detrimental to the evenness of a coating spread by the resulting doctor blade, and dividing the so-chamfered blank into doctor blades of suitable lengths. 2. As a new product a coating doctor blade having a chamfered coating-containing surface, said doctor blade haVing been made by the process defined in claim 1. 

2. As a new product a coating doctor blade having a chamfered coating-containing surface, said doctor blade haVing been made by the process defined in claim
 1. 